Macular degeneration is a retinal disease which is the leading cause of central vision loss among people over the age of 65. Macular degeneration is a process of wear and tear in the macula, the portion of the retina responsible for sharp central vision and color perception. It usually affects both eyes, causing vision loss which may be either gradual or abrupt.
Referring to FIG. 1, a cross sectional view of a human eye is shown. The human eye is designed for panoramic viewing, allowing an individual to see objects straight ahead as well as to the side. As light enters the eye 10, it passes through the cornea 11 and pupil 12, and is focused by lens 13 into an image on retina 14. This image is converted by the retina into electrical impulses which are transmitted via optic nerve 15 to the brain. Macula 16 is the particular portion of the retina at which sharp central vision is processed.
The macula consists of multiple layers as is shown in FIG. 2. Innermost layer 18 of macula 16 is comprised of light sensing cells which produce sharp central vision. Two underlying layers nourish and help remove waste materials from these light sensing cells. The light sensing cells or "cones" as they are commonly referred to, are responsible for color perception and central vision. These cones shed their outer segments as waste products through normal metabolism. Second layer 20, known as the "retinal pigment epithelium", nourishes the cones and digests these shed outer segments during the day. Finally, third layer 22, known as the "choroid", comprises blood vessels that transport nutrients and carry away waste material from the macula region.
Macular degeneration is the common name for the age-related disease where macular retinal pigment epithelium cells function less well than normal. As a result, waste removal and nutrition of the cones suffers, causing central vision loss. Macular degeneration can be further classified into two varieties: a "dry type" and a "wet type". Dry type macular degeneration occurs when the outer segments of the light sensing cones, which are continuously being shed, are unable to be digested by the pigment epithelium layer of the macula. Consequently the pigment epithelium layer swells and eventually dies after accumulating too much undigested material from the cones. Yellowish deposits of this waste material gradually develop under the retina between the choroid and pigment epithelium. In this "dry type" macular degeneration, the vision loss is characterized by gradual blurring or partial obscuration of central vision as a result of parts of the macula having begun to die, creating areas where the cones are no longer functional. Clinically, the person suffering from this type of the disease may experience relatively mild central visual distortion with straight lines appearing bent or wavy.
In the second or "wet" type of this disorder, more severe and sudden vision loss may occur. This sort occurs when abnormal new blood vessels or "neovascular membranes" grow from the choroid through the damaged pigment epithelium and under the macula. These neovascular membranes are fragile and are prone to hemorrhage which results in severe distortion of the macular tissue. As a result, the light sensing cells (cones) become separated from their source of nutrients and suffer further damage due to eventual scarring as the hemorrhage contracts over time. With this type of disorder, dark or "missing" spots in the central vision may occur rapidly and with little warning due to these hemorrhagic changes. Fortunately, intervention with laser therapy early in this process may often prevent additional vision loss.
In order to detect changes early enough such that laser is beneficial, doctors use a variety of tests designed to evaluate the health of the macula. One such test is termed the "Amsler grid" and utilizes a uniform grid pattern of crossing lines to test central vision. The use of this grid reveals distortions and other abnormalities in the central field of vision. A patient once having been diagnosed with macular degeneration is typically required to monitor their vision with an Amsler grid on a daily basis in order to detect subtle signs of increasing distortion which may indicate an evolving neovascular membrane. Since this "wet" form of the disease may occur suddenly and with rapid vision loss, daily follow up is essential to ensure that intervention with laser treatment is instituted early enough to help prevent further visual damage.
The Amsler grid is known in the art (See FIG. 3). The use of the Amsler grid requires that a patient stand about a foot away from the grid itself, and, while wearing one's own glasses, covering or closing one eye while focusing on the center of the grid. In order for the Amsler grid to be effective, the patient must note any changes that occur over time and repeat the above process on a daily basis. While Amsler grids have been known for years in the art, the use of the grid in a practical setting by patients has revealed a number of every day problems.
Because of the nature of this degenerative eye disorder, daily use is required in order to track changes associated with the disorder such that early effective treatment can be implemented. As such, the grid must be accessible and easy to use in order to encourage use of the product. Accordingly, any improvements to the design of the grid which would improve the overall accessibility and ease of use would facilitate regular use. Use by patients has revealed that improvements to the basic grid design which facilitate the daily use of the device result in more consistent use of the product.
Secondly, the grid must also be sufficiently sized to accommodate the self testing of both the user's central and peripheral vision. A grid which is too small won't allow for the evaluation of a sufficient field of vision, yielding inaccurate or incomplete test results. However, the grid must not be so large as to become a nuisance to manipulate or store.
The degenerative nature of the eye disorder also requires that a patient be able to monitor the progress of the disease by somehow recording the particular areas of concern associated with each of the patient's eyes for a given baseline time frame, in order to determine whether or not any further damage has arisen. While the original grids were mass produced on paper products, any improvement which would assist the patient to identify and log the current eye condition as compared to a baseline condition would be desirable in order to help the patient in evaluating changes to his or her vision.
As described previously, the basic architecture of the Amsler grid includes a grid area which is utilized by the patient to assist in the evaluation of their vision. In practice patients have suggested that because of the poor contrast of the fixation target of the grid, that they often find themselves, and their eye that they are testing, wandering after but a few brief seconds when using the grid. Accordingly, any means of helping to assist a patient to keep their attention focused toward a single central location on the grid would assist in improving the accuracy of the self diagnostic tool.
The present invention improves on the prior art by providing a central attention focusing means which is designed to hold the patient's attention squarely centered on the grid so as to allow for a more accurate self diagnosis. The present invention includes an erasable re-writable surface to assist patients in identifying changes to their vision and progression of the disorder. The present invention also packages the grid, central focusing means and re-writable surface in a package which will assist the patient in performing the test on a daily basis, helping to remind the patient to conduct the self diagnosis while minimizing the possibility of loss of the grid itself and the baseline information upon which is stored.